1. Field of the Invention
A communication system according to the present invention is established on the assumption that lines between an exchange unit 1200 and cell stations 200 and between the exchange unit 1200 and a concentrator 300 comprise existing subscriber lines (i.e., the exchange unit 1200 is connected to each of the cell station(s) 200 and the concentrator 300 through the subscriber lines), and the exchange unit 1200 is further connected through the cell stations 200 or the concentrator 300 to WLL (Wireless Local Loop) fixed terminals (e.g., personal stations: hereinafter referred to as "PS") whose number is larger than the number of subscriber lines (see FIG. 1). Therefore, the one-to-one corresponding relationship is not established between the subscriber lines and the WLL fixed PS serving as a subscriber PS, and thus correct billing cannot be performed on each WLL fixed PS in a conventional exchange unit system because the conventional exchange unit system has charged the fee for a telephone call merely on a subscriber line basis. Therefore, the present invention relates to a communication system using personal stations (PS), and particularly to a collecting technique for billing information in a communication system in which a communication route between a communication network and a concentrator or a cell station (CS) comprises an existing analog line.
2. Description of Related Art
A simple portable telephone system, known as a PHS (Personal Handy Phone System), has been practically used as a communication system using personal stations (PS). The PHS system basically comprises personal stations (PS), cell stations (CS) which are connected to the personal stations (PS) through wireless digital lines, a concentrator which is connected to plural cell stations (CS) through lines, and a network which is connected to the concentrator and the cell stations (CS) through lines.
The PHS system is established on the assumption that it uses a signal system based on ISDN (Integrated Services Digital Network) which is a kind of digital line. Like the ISDN, the signal system generally has a B-channel for transmitting information of a telephone call such as voice or the like and a D-channel for control information, and the B-channel and the D-channel are designed independently of each other. Therefore, according to the PHS, a control signal containing information required for authentication information and billing between a network and a cell station is transmitted and/or received through the D-channel of the signal system while telephone voice is transmitted and/or received through the B-channel, whereby the control signal and the telephone voice can be transmitted or received in parallel on the time axis (e.g., simultaneously).
The infrastructure located near to the subscriber personal station (hereinafter referred to as "subscriber PS") of a Public Switching Telecommunication Network (PSTN) needs the highest cost compared to the other portions, and also needs more time for laying. In view of this problem, in order to lay a low-cost and high-speed infrastructure, a wireless line used for portable telephone may be used as a wireless subscriber line for a part of an existing subscriber line which is near to a subscriber PS. With respect to the existing subscriber line, only one subscriber line is allocated to each subscriber. Therefore, if billing is performed on a line basis, the billing is also performed on a subscriber basis. Further, in this case, in consideration of minimizing alteration of the facilities of an existing exchange and suppressing the cost-increase, there may be a case where an existing analog subscriber line is used between a cell station (CS) and a network or between a concentrator and a network. However, there is the following characteristic of the wireless line as a wireless concentrating effect:
(the number of subscribers belonging to a cell station)&gt;(the number of wireless lines)
As described above, the one-to-one corresponding relationship is not established between the line and the subscriber. Therefore, when the billing is made to each subscriber at the exchange unit side, it is required for every call that discrimination information on a calling side, for example, a PS number (subscriber number) is notified to the exchange unit.
In the case of the ISDN, the notification of the PS number can be performed on a real-time basis because a signal line and a telephone path are separately provided. Therefore, the billing can be performed in an exchange unit as disclosed in Japanese Laid-open Patent Application No. Hei-6-217365 or a data base connected to the exchange unit. However, when a line accommodated in an exchange unit is an existing analog line as described above, a tone signal may be used to notify a subscriber number (PS number). However, in this method, a connection delay occurs at the time of calling, and there may occur a case where a line connection cannot be established due to time-out of a connection standby timer in accordance with the regulations of a network or an exchange unit to be connected.
Further, PS (personal station) authentication processing which is one characteristic processing when a wireless line connection is carried out, and is performed between a PS and an exchange unit or a network, also requires signal transmission/reception for every call on a real-time basis at the time of line connection, however, this requirement cannot be satisfied for the reason described above.